Support Linux DRM backend by Bennctu · Pull Request #69 · sysprog21/mado

Bennctu · 2024-11-03T14:58:55Z

Currently, using the DRM legacy interface is suitable for Mado's backend because we only need basic window display without advanced features.

jserv · 2024-11-11T02:48:58Z

Check the DRM implementation for reference: https://github.com/zlgopen/awtk-linux-fb/blob/master/awtk-port/lcd_linux/lcd_linux_drm.c

huaxinliao · 2025-01-26T16:32:31Z

+    twin_screen_resize(SCREEN(ctx), width, height);
+}
+
+static void twin_drm_exit(twin_context_t *ctx)


I consider that twin_drm_exit should handle ioctl(tx->drm_dri_fd, DRM_IOCTL_MODE_DESTROY_DUMB, &destroy) to ensure allocated resources are properly released.

jserv · 2026-05-01T12:05:56Z

For mado, a libdrm-free DRM backend is realistic because the use caseonly needs KMS + dumb buffer + CPU rendering, not GBM/EGL/GPU rendering. This pull request currently uses libdrm helpers such as drmModeGetResources, drmModeGetConnector, drmModeAddFB, drmModeSetCrtc, and drmModeRmFB, while already using raw ioctls for dumb-buffer creation/mapping.

The dumb-buffer path is appropriate: DRM dumb buffers are CPU-mappable scanout buffers, suitable for simple rendering but not complex GPU composition. GETCONNECTOR is intentionally a two-pass ioctl: first retrieve counts, then allocate arrays and retrieve modes/encoders; hotplug can race, so retry until counts stabilize.

Minimal ioctl-only framebuffer sequence is shown below:

open("/dev/dri/card0", O_RDWR | O_CLOEXEC);

DRM_IOCTL_MODE_GETRESOURCES;
DRM_IOCTL_MODE_GETCONNECTOR;   /* two-pass */
DRM_IOCTL_MODE_GETCRTC;

DRM_IOCTL_MODE_CREATE_DUMB;
DRM_IOCTL_MODE_ADDFB2;
DRM_IOCTL_MODE_MAP_DUMB;
mmap();

DRM_IOCTL_MODE_SETCRTC;

Use legacy SETCRTC first, not atomic KMS. Atomic is cleaner long-term, but it requires property discovery and more code. For mado’s CPU-rendered full-screen backend, direct legacy KMS ioctls are the smallest maintainable step.

Bennctu · 2026-05-01T17:09:35Z

I ran the DRM backend on a VM with Ubuntu 24.04. However, I noticed that the screen froze.
drm.mov

I verified that the DRM backend runs successfully on Ubuntu 24.04 VM.

Screencast.from.2026.02.00.56.24.webm

huaxinliao · 2026-05-01T17:38:35Z

I'm curious which part of the code fixed the VM issue.

huaxinliao · 2026-05-01T17:55:21Z

Currently, using the DRM legacy interface is suitable for Mado's backend because we only need basic window display without advanced features.

Hi @Bennctu, Also, does commit e4f93e9 show the same rendering result as this one? I’d like to learn more about this part as well. Thank you for your generous explanation!

Implemented DRM-based framebuffer setup, including: - Opening the DRM device - Creating dumb buffers and mapping them to framebuffers - Setting mode and handling CRTC for connected display output The legacy DRM ioctl interface is used as the current implementation does not require atomic mode-setting or page flipping. Atomic mode-setting prevents inconsistent states, supports rollback on failures, and enables mode testing before committing changes. Atomic page flipping synchronizes multiple planes within a VBLANK interval, preventing tearing and improving display updates, especially for power-efficient embedded controllers. While the atomic API enhances KMS with property-based state management, its complexity is unnecessary for now. The legacy interface remains adequate, but future needs may justify adopting atomic mode-setting. Close sysprog21#60

cubic-dev-ai

1 issue found across 5 files

Prompt for AI agents (unresolved issues)


Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="configs/Kconfig">

<violation number="1" location="configs/Kconfig:81">
P2: `BACKEND_DRM` is missing a dependency gate for libdrm, so users can enable it in Kconfig and hit build failures on systems without libdrm installed.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

cubic-dev-ai · 2026-05-07T14:28:56Z


+config BACKEND_DRM
+    bool "Linux DRM support"
+    depends on !CC_IS_EMCC


P2: BACKEND_DRM is missing a dependency gate for libdrm, so users can enable it in Kconfig and hit build failures on systems without libdrm installed.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At configs/Kconfig, line 81: <comment>`BACKEND_DRM` is missing a dependency gate for libdrm, so users can enable it in Kconfig and hit build failures on systems without libdrm installed.</comment> <file context> @@ -76,6 +76,15 @@ choice +config BACKEND_DRM + bool "Linux DRM support" + depends on !CC_IS_EMCC + select CURSOR + help </file context>

jserv · 2026-05-09T20:19:38Z

Thank @Bennctu for contributing!

jserv reviewed Nov 3, 2024

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Bennctu force-pushed the drm_dev branch from f8729f4 to 8cd4c32 Compare November 6, 2024 16:30

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a1091150 mentioned this pull request Nov 7, 2024

Fix memory region in framebuffer #65

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Bennctu force-pushed the drm_dev branch 2 times, most recently from 32e2217 to 3cba956 Compare November 23, 2024 07:19

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Bennctu force-pushed the drm_dev branch 2 times, most recently from f711c33 to e275994 Compare January 22, 2025 13:51

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Bennctu force-pushed the drm_dev branch from e275994 to e4f93e9 Compare May 1, 2026 16:46

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jserv merged commit c2f8231 into sysprog21:main May 9, 2026
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Bennctu commented Nov 3, 2024 •

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